Fluid energy milling solid granular material



United States Patent inventor Nicholas N. Stephanofl Haverford. Pa.Appl. No. 813,590 Filed Apr. 4, 1969 Division of Ser. No. 455,265, May12, 1965, Patent No. 3,456,887. Patented Dec. 29, 1970 Assignee FluidEnergy Processing 8: Equipment Co.

Lansdale, Pa.

a corporation of Pennsylvania FLUID ENERGY MILLING SOLID GRANULARMATERIAL 6 Claims, 9 Drawing Figs.

US. Cl 241/5 Int. Cl. B02c 19/06 Field of Search 241/5, 39, 40

References Cited UNITED STATES PATENTS 2,735,626 2/1956 Trost 241/39Primary Examiner-Robert C. Riordon Assistant Examiner-Donald G. KellyAttorney-Arthur A. Jacobs ABSTRACT: The pulverization of solid particlesby propelling two opposed streams of the particles against each other bymeans of high-pressure fluids. The impact between the particles iseffected in a central impact chamber which is in communication with aperpendicular stack. The pulverized particles pass through thisperpendicular stack and are separated into two opposed streams. Theopposed streams pass in opposite directions through opposed centrifugalmills where separation of the lighter and heavier particles takes place,and from each of which the heavier particles are returned to the impactchamber for further impacts with each other as they travel in opposeddirections.

PATENTEU UEB29 I976 SHEET 1 OF 3 INVENTOR. Nicholas N. Stephanoff A TTOEE Y PATENTED UEE29 I970 SHEET 2 OF 3 INVENTOR. Nicholas NS fePhunoH.

ATTORNEY PATENTEU'UEEZS m0 SHEET 3 OF 3 INVENTOR. Nicholas N. Sraphano AT TORNE Y FLUID ENERGY MILLING SOLID GRANULAR MATERIAL This is adivision of applicationSer. No. 455,265, filed May 12, 1965, issued asU.S. Pat. No. 3,456,887 on Jul. 22, 1969.

This invention relates to a method and apparatus of grinding orpulverizing solid material, and it particularly relates to the so-calledfluid energy method of grinding wherein a high velocity elastic fluid,such as a gas or vapor, is utilized as the grinding medium.

The ordinary fluid energy type of grinding mill comprises a curved orannular duct having a feed inlet adjacent the bottom portion for feedingthe grandular solid raw material into the mill and a plurality oftangentially arranged inlet nozzles at the bottom through which theelastic fluid is inserted at high velocities. This bottom portionconstitutes the primary grinding chamber wherein the raw solids arecaught up and hurled against each other by the incoming gaseous fluidswhich form a vortex because of the tangency of the fluid nozzles. Thesolid particles are pulverized by these impacts. The pulverizedparticles, because of the centrifugal force imparted thereto by the highvelocity gases, together with the gaseous vortex, are impelled upwardlyfrom the bottom grinding chamber through the so-called upstack portionof the curved or oval mill. The less finely ground particles, beingrelatively heavy,'are impelled by their centrifugal force to the outerperiphery of the vortex and continue to pass through the mill inaccordance with the curvature thereof. The more finely ground particles,being relatively light, are entrained in the gaseous vortex and arecarried by the viscous drag of the gases around the inner periphery ofthe mill. As the solid particles and gaseous vortex pass around theupper portion of the the mill and then into the curved classifierportion, the lighter particles are carried by the used up gases, orthose which have lost a large part of their vortex energy, through anoutlet duct opening from the inner periphery of the mill to a collectionstation, whil'ethe heavier particles and remaining vortex gases arecarried by their centrifugal force around the outer periphery back tothe grinding chamber where the heavier particles are again subjected toimpact by freshly fed solids.

The above described type or of apparatus, although greatly moreeffective for its purposes than other heretofore known grinding devices,has certain disadvantages which prevent the full and most effectiveutilization of the fluid energy grinding method. For example, althoughthe grinding or pulverizing effect of this method largely depends on themomentum produced on the particles by the high velocity gases, it hasrarely been possible, heretofore, to achieve a fluid velocity in thegrinding chamber evenapproximating the velocity of the fluid enteringthrough the nozzles. One of the main reasons for this is that when thefluid issuing from the nozzles picks up the solid particles from thefeed means, the fluid must expend a substantial portion of its ownenergy in order to provide an impetus on the particles. Furthermore, inorder to entrain the particles, it is necessary to effect an expansionof the fluid as it leaves the nozzle so that c'ircumvallating eddycurrents are formed which suck the solid particles into the fluid.Without such eddy currents, the velocity of the fluid as it leaves thenozzle would be so high that a high intensity dynamic barrier would beformed therearound. This barrier would prevent entrance of the particlesinto the fluid stream. Conversely, the decrease in fluid velocitydeleteriously effects the number and force of impacts between theparticles and results in a diminution in possible grinding effect.

In addition, the use of tangentially or angularly arranged fluidnozzles, while necessary to form the fluid vortex and'to impel theparticles through the mill, permitted the particles to collide with eachother at relatively acute angles whereby there were often only glancingblows between the particles so that the full force of head-on collisionswas lost and the resultant grinding or pulverization was less effective.

Moreover, in the curved or oval mill, it has been found that the maximummill circulating velocity obtainable is about 25 percent that of thevelocity of the fluid as it leaves the inlet I nozzle. This is due tothe fact that although the velocity of the fluid and particles on theouter periphery of the vortex is increased because of their centrifugalforce, the velocity on the inner periphery is so low as to measure zeroor even negative velocity at times, especially when an insufficientamount of fluid enters through the nozzles so that there is not enoughcir culating fluid to fill the void created by the centrifugally outwardshift of the fluid. The total velocity of the circulating fluid is,therefore, considerably diminished relative to the en trance velocity.In practice, the circulation also depends, to some extent, on thefrangibility of the material being processed, the weight and size of theparticles, and the amount and rate of feed of the material, the heavierthe load borne by the fluid, the slower the circulation.

It is, however, most desirable to obtain as rapid a circulation aspossible because the higher the velocity, the more vigorous the vortexturbulence and the greater the degree of separation of the lighter finerparticles from the heavier coarser particles. However, in the ordinarymill, not only isthe velocity of the fluid diminished for the abovereasons but the more rapid the circulation the less grinding effect isobtained due to the fact that the grinding is caused by opposed impactof the particles against each other whereas the circulation moves theparticles in the same direction and, therefore, decreases theprobabilities of impact.

- and, therefore, the maximum separation and classification of 'platesshown in FIG. 5.

finer and coarser particles is obtained.

Another object of the present invention is to provide a method andapparatus of the aforesaid type which can be effectively utilized notonly for grinding or pulverization but also for various other purposessuch as coating, mixing, metallizing cold-welding, etc.

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the same becomes better understood byreference to the following description when read in conjunction with theaccompanying drawings wherein:

FIG. 1 is a sectional view of anapparatus embodying the presentinvention.

FIG. 1A is a cross-sectional view taken on line lA-IA of FIG. 1.

FIG. 2 is a fragmentary sectional view of a modified form of theapparatus of FIG. 1.

FIG. 3 is a sectional view of a second embodiment of the presentinvention.

FIG. 4 is a sectional view of a-third embodiment of thepresentinvention.

FIG. 5 isa sectional view of a fourth embodiment of the presentinvention. Y

FIG. 6 is a front elevational view of oneof the nozzle orifice FIG. 7 isa sectional view of a modified form of the apparatus shown in FIG. 5. 1

FIG. 8 is a sectional view of another modified form of the apparatusshown in FIG. 5.

In accordance with the present invention, two opposing streams of highvelocity fluid having substantially the same linear velocity andintensity and having solid particles entrained therein, are directedtoward each other to impact at a common intermediate or central impactarea. A common upstack or downstack, as the case may be, leads from theimpact area into separate and opposed curved classifier sections wherethe finer particles 'are separated and passed to a collection stationwhile the heavier particles are recycled through separate and opposedretum'ducts back into the respective opposed fluid streams forregrinding.

It is highly important that the two opposing streams be of substantiallyequal velocity and strength since only in this manner can the maximumopposed kinetic energy be utilized to secure maximum impact and,therefore, maximum pulverization. As a consequence it is also importantthat there be a common upstack (or downstack) leading laterally from thecentral, intermediate, common impact area since the full energies of thetwo fluid streams, after impact, merge and are directed laterally intothe upstack. This maximum energy is translated into a rapid movement ofthe fluid vortex and pulverized particles through the upstack and aroundinto the classifier section and then back through the return ducts. Inthis manner, not only is maximum grinding or pulverization obtained butalso maximum circulatory velocity and, therefore, maximum separation andclassification of the fluid and solid particles.

Referring now in greater detail to the various FIGS. of the drawingswherein similar reference characters refer to similar parts, there isshown in FIG. 1 a mill, generally designated 10, comprising a straightgrinding chamber 12 having an inlet duct 14 at one end and an opposedinlet duct 16 at the opposite end. The chamber 12 is preferably providedwith a trapezoidal cross-sectional contour, such as shown in FIG. 1A,wherein the lower portion is relatively narrow and the sides taperupwardly and outwardly to a relatively wide upper portion. With thistype of cross-sectional configuration, if there is less than a maximumamount of material in the chamber it will be concentrated in the lowerportion of the chamber so that the probabilities of impact between theparticles will be greater. However, the grinding chamber 12 may also beof circular configuration or of any other configuration which isdesirable and feasible.

The ducts l4 and 16 are identical, each comprising a Venturi tube withone end opening into the grinding chamber 12 and the other end beingclosed except for an aperture through which projects an inlet nozzle,indicated at 18 and 20 respectively. Each inlet nozzle 18 and 20 isconnected to a source (not shown) of elastic fluid (gas or vapor) underhigh pres sure. A hopper, as at 22 and 24 respectively, opens downwardlyinto the respective venturi duct adjacent the inlet end of therespective nozzles 18 or 20.

At the center of the grinding chamber 12 is provided a central impactarea 26 substantially equidistant from the two opposed ducts 14 and I6.Extending upwardly from this impact area 26 is a common upstack 28 whichmay be either of the same cross-sectional shape as shown in FIG. 2 or ofcircular or other desirable shapes. The upstack, at its upper end,divides into two separate and oppositely curved arcuate classifiersections, respectively designated 30 and 32, which are preferablycircular or oval-shaped but which may be of the same crosssectionalshape as the upstack 28. These classifier sections 30 and 32 are eachprovided with an exhaust duct, as at 34 and 36 respectively, which leadto a common or separate collection stations. Each classifier sectionalso merges with a corresponding return section, as at 38 and 40respectively, leading back into the grinding chamber 12 adjacent therespective duct 14 or 16.

A pair of annular headers 42 and 44, one on each side of the centralimpact chamber 26, are optionally provided. These plates are connectedto a source of elastic fluid under pressure and each is provided with atleast one, but preferably a plurality, of nozzles, designated 46 and 48respectively, which extend into the grinding chamber 12 and act as highpressure fluid nozzles. Fluid jets from these nozzles, entering thegrinding chamber, serve as boosters to accelerate the flow of theopposed streams before they collide in the impact chamber.

Instead of an upstack, a downstack may be used with correspondingclassifier and return sections, whereby the apparatus would be a reverseform of that shown in FIG. 1 but would function in the same manner..

The solids feed means are here illustrated as hoppers for gravity feed.However, any other desirable and feasible type of feed means can besubstituted such as a screw feed, a fluid pressure or suction feed, arotary valve type feed, etc.

In operation, high velocity streams of elastic fluid such as compressedair, steam, or the like, are passed through the nozzles 18 and 20, theforce of the two streams being substantially equal so that they impactin the central area 26. At the same time, solid particles are fedthrough the hoppers 22 and 24 and are entrained in the high velocityfluid streams, adjacent the inlets of the respective nozzles 18 and 20.The two fluid streams, with the solid particles entrained therein, thenpass through the venturi ducts, which increase their velocity, into thegrinding chamber 12 where they impact at 26. Since the particles collidehead on, rather than with glancing blows as in the case where tangentialfluid nozzles are used, and since the forces of momentum thereon aresubstantially equal and opposite, the maximum amount of pulverization isobtained.

As indicated above, the orifice plates 42 and 44 are optional and thereis no necessity, in most cases, for the their use. However, in thosecases where it is desirable to use them in order to further increase thevelocity of the opposed streams, they are very effective in restoringmost, if not all, of the velocity lost by the fluid in entraining andmoving the solid particles fed thereinto. I

Since the upstack 28 leads directly from the central impact chamber orarea 26, the fluid vortex resulting from the impact and the solidparticles, both of which constitute the impact residue, pass directly upthrough the upstack under maximum energy conditions. Consequently, thecirculatory forces are at a maximum.

When the fluid vortex and solid particles reach the upper end of theupper end of the upstack 28, one part thereof passes through theclassifier section 30 and the other part passes through the classifiersection 32. The larger, heavier particles, having a greater centrifugalforce, remain on the outer periphery of the fluid vortex and pass downthrough the return sections 38 and 40 to the grinding chamber 12 wherethey are caught up in the fluid streams issuing from the ducts l4 and16. The smaller, lighter particles are caught up by the viscous drag ofthe vortex fluid and remain on the inner periphery thereof to be carriedout through the exhaust ducts 34 and 36.

It should be noted that the classifier and return sections arepreferably of gradually diminished width because as man many of thesolid particles become ground into finer sizes requiring less space, andare then exhausted, leaving still more space, the reduction in width ofthe ductwork acts to better concentrate the particles of relativelylarge size and fluid being recycled.

In FIG. 3 there is shown a modified form of the invention wherein theapparatus is essentially similar to that of FIG. 1 except that theventuri portions of the opposed fluid pressure nozzles are incorporateddirectly into the grinding chamber and the return ducts lead directlythereinto instead of into the separate venturi passages shown in FIG. 1.

In FIG. 2 there is shown a modified form of the apparatus of FIG. 1wherein the opposite portions of the grinding chamber 12A are inclinedupwardly toward the impact chamber 26A from which leads the upstack 28A.

This inclination is sometimes desirable because it-provides an upward aswell as horizontal movement of the opposing streams which increases theupward velocity of the impact residue through the upstack 28A and,therefore, increases the circulatory velocity through the apparatus.

The apparatus of FIG. 3 is generally designated 50 and comprises opposednozzles 52 and 54 leading from a source of high pressure elastic fluid(not shown) into the otherwise closed ends, shown at 56 and 58respectively, of a grinding chamber 60. The ends 56 and 58 arerelatively wide and are each provided with a solids feed inlet, as at 62and 64.

Extending between each end 56 and 58 and a central impact area orchamber 66 is a relatively narrow throat portion, as at 68 and 70respectively, from 'which extends a gradually widening passage, as at 72and 74 respectively. This construction provides a pair ofoppositely-disposed venturi passages which actually serve as opposedconvergent-divergent nozzles for propelling the fluid streams, withthe-particles entrained throat portions 68 and 70. Since the pressure inthese throat portions is at a minimum, there is a suction effectprovided that helps draw. the return fluid and particles into theopposed impacting streams and, therefore, increases the return flowwhich, in turn, increases the circulatory flow.

The grinding chamber in this form of the device and in thosehereinafterdescribed, are of circular rather than trapezoidal shape but atrapezoidal shape may be used, if desired.

In FIG. 4 there is illustrated a form of the invention which is similarto that of FIG. 3 except that the solids feed inlets lead directly intothe return ducts. By passing the'solids directly into the return ducts,the particles are given an initial acceleration which is added to thefurther acceleration provided by the fluid inlet nozzles, therebyincreasing their velocity and providing a greater circulatory velocity.

The particular structure embodying this form of the invention, as shownin FIG. 4, comprises a mill, generally designated 100, having a grindingchamber 102 with opposed high-pressure fluid nozzles .104 and 106 atopposite ends 108 and 1100f the grinding chamber 102. The grindingchamber 102 then narrows to form throats 112 and 114, after which itagain widens from either end toward the relatively wide central impactarea 116, whereby a venturi or convergent-divergentduct is formed. Anupstack 120 leads from the central im- 1 pact area 116 upwardly to anupper end where it divides into two oppositely curved classifiersections l22and 124. Each classifier section 122 and 124 is providedwith an exhaust duct, as at 126 and 128 respectively, and then mergeswith a return duct, as at 130 and 132.

Each return duct 130 and 132 is provided witha solids feed inlet, as at134 and 136. respectively. The inlets 134 and 136 are illustrated asbeing of the venturi type with fluid pressure nozzles, as at 138 and140, leading thereinto from a source of high pressure fluid (not shown).The high-pressure fluids from the nozzles 138 and 140 entrain the solidparticles from the hoppers of inlets 134 and 136 and are then givenincreased velocities as they pass through the inlet venturi passages.However, any other type of desirable feed means, such as screw feeders,rotary valve feeders, and the like, may be substituted.

The fluid streams with the entrained solid particles pass through theinlets 134 and 136 and are caught up by the circulating fluid vortexdescending the respective return ducts so that the fed raw materialsreceive an added impetus prior to entering the grinding chamber 102 andthen receivea further impetus as they pass through the throats 112 and114 of the grinding chamber.

In FIG. 5 there is shown a form of the invention, generally designated150. that comprises a grinding chamber 152 similar to that shown at 102in FIG. 4 in that it comprises two opposed venturi orconvergent-divergent sections, one on each side of the central impactarea 154, each encompassing a throat portion, as at 156 and 158respectively. Intermediate each throat portion and the correspondingreturn duct is an annular header or orifice plate. as at 160 and 1 62respectively. Each of these. headers. shown in front elevationin FIG. 6,is in fluid connection with a source of elastic fluid under pressure(not shown) and is provided with at leastone, but preferably aplurality,of tangential orifices indicated at 164 for plate and at 166 for plate162.

The central impact area opens up into the common upstack 168 leadinginto the oppositely curved classifier sections 170 and 172, providedwith exhaust ducts 174 and 176 respectively, and leading into returnducts 178 and 180 respectively.

Solids feed inlets I82 and 184, similar to inlet inlets 134 and 136, areconnected to the respective return ducts 178 and 180.

In this fonn of the apparatus, the opposed fluid nozzles are entirelyeliminated and only the circulatory velocity of the fluid passingintothe grinding chamber from the return ducts is utilized. However, notonly is a large amount of energy expended by the fluid in 'entrainingand moving the solids fed through the inlets 180 and 182, as explainedabove, but, in addition, some of the. circulating fluid is lost byexhaustion through the exhaust ducts. The orifices 164 and 166 are,therefore, used not only as booster nozzles to increase the velocity ofthe fluid as it passes from either end of the grinding chamber towardthe central impact area, but also to replenish spent and exhaustedrecycling fluid. The convergent-divergent construction of the twoopposite portions of the grinding chamber also aids in increasing thevelocity of the fluid.

Between each of the return ducts 220 and 222 and its respective chamberportions 204 and 206 are provided at least two orifice plates,designated 224 and 226 on the one side and 228 and 230 on the other.Between the plates 224 and 226 is a I duct portion 232 which tapersinwardly so that it forms a socalled abrupt nozzle section between thetwo orifice plates. The same is true of the opposite duct portion 234between the orifice plates 228 and 230. These abrupt nozzle portions,supplied with high pressure elastic fluid from the orifices in their Vrespective plates 224 and 228, boost the velocity of the return fluidfrom the respective return ducts 220'and 222 back to approximatelyacoustic velocity. This boosted fluid then receives a further boost intothe superacoustic velocity range as it passes through the throatportions of the chamber sections 204 and 206 where they are subject tothe additional force of the high-pressure elastic fluid issuing from theorifices of the respective plates 226 and 230.

i The orifice plates 224, 226,. 228'and 230 are connected through valvedconduits to a manifold 236 which is, in turn, connected to a source offluid under pressure not shown).

The solids feed is provided by inlets 238 and 240 connected to therespective return, ducts 220 and 222, these inlets being preferably ofthe same type as those shown in FIGS. 4 and 5.

Although two orifice plates are illustrated at each side, it is to beunderstood that as many as desired may be used in series, depending onthe amount of boosting action desired.

The apparatus of FIG. 7 is particularly adapted for most effectivetreatment of large, heavy or relatively nonfrangible solid particlesthat require the force supplied by superacoustic velocities. However,where smaller, lighter or more frangible material is being processed, itis usually preferable to use an apparatus such as illustrated in FIG. 8.

The apparatus of FIG. 8, generally designated 250, is very similar tothatof- FIG. 7 in that it includes-a central impact area 252 from'whichleads an upstack 254 dividing into oppositely-curved classifier sections256 and 258 having respective exhaust ducts 260 and 262' and leadinginto return ducts 264 and 266 that are. respectively provided'withsolids inlets 268 and 270. It' is also similar in that between each ofthe respective return ducts and their respective opposed grindingchamber sections 272 and 274 there is provided a pair of ori-.

effect is in the vicinity of acoustic velocity rather than superacousticas in the apparatus of FIG. 7.

In this apparatus, too, the number of orifice plates in series on eachside may be varied as desired.

As indicated above, although the apparatus described herein has beenillustrated in each case as having a central upstack with consequentupwardly circulatory movement. it is equally within the scope of thepresent invention to use a central downstack with downwardly circulatorymovement.

The invention described above has been illustrated as utilizable forgrinding or pulverization of solid particles. However, any of the abovedescribed apparatus can also be used for effective mixing of differenttypes of particles as well as for coating particles whereby theparticles to be coated are projected from one side and the coatingmaterial from the other so that coating is effected by impact under thehigh velocities present. in the same manner, particles can be metallizedor cold-welded together. This apparatus may also be used for the removalof liquids and for dehydrating, especially if additional heat isprovided. Such additional heat energy may be provided by heated elasticfluids or auxiliary heating means. it is. furthermore, possible toeffect certain chemical reactions in this manner without the heat energyusually required although. if desired, heat energy can be simultaneouslysupplied by using heated elastic fluids or auxiliary heating means inthe grinding chamber. In this respect, it is to be noted that liquidsfor coating. chemical reaction, quenching, etc. may be ejected throughthe booster orifices into the fluid and particle streams, if so desired.

It is further to be noted that although the apparatus, as describedabove, has, in each case, consisted of two opposed ductworks, it iswithin the scope of the present invention to provide three or moreopposed impact streams intersecting at a central impact area and acorresponding number of three or more recycling ductwork systems.

Obviously, many modifications of the present invention are possible inthe light of the above teachings. it is, therefore, to be understoodthat within the scope of the appended claims,

the invention may be practiced otherwise than as specifically described.

lclaim:

1. A method of treating solid particles which comprises propelling atleast two fluid streams with solid particles entrained therein towardeach other at substantially equal velocities to effect an impact at acentral impact area, passing the impact residue comprising the resultantfluid and both lighter and heavier solid particles away from said impactarea in a direction transverse to the directions in which said fluidstreams were propelled toward each other, dividing said impact residueinto at least two diverging streams, separating and removing the lighterparticles from said diverging streams, intermixing each of saiddiverging streams with fresh solid particles and propelling each of theresultant mixtures toward each other at substantially equal velocitiesto effect further impact at said impact area.

2. The method of claim 1 wherein said diverging streams of impactresidue are each entrained in a fresh mixture of fluid and solidparticles while said fresh mixtures are being propelled toward eachother.

3. The method of claim 1 wherein said fresh solid particles are added tothe respective diverging streams prior to the entrainment of saiddiverging streams in fresh propelled fluid streams.

4. The method of claim 1 wherein each of said resultant paths of traveltoward each other.

6. The methods of claim 1 wherein said resultant mixtures are propelledtoward each other at initial velocities which are increased by passingeach of said resultant mixtures through at least one constrictedpassage.

